Stabilize first-run cudagraph timing and colorize terminal output

- _cudagraph_plugin: warm up autotune/JIT explicitly before graph capture
  (internal 5-iter warmup is too short), tag fallback markers with the
  failing phase; first-run latency no longer jitters run-to-run.
- _device_guard_plugin (new): set GEMS_VENDOR via torch probe before
  importing flag_gems, avoiding its timeout-less nvidia-smi subprocess
  probe that can hang import in fork-broken environments.
- _pretty_report_plugin (new) + _term_style (new): fold inputs identical
  across all result rows into a legend line, color status/plugin
  tags/markers on the live terminal; run.log is ANSI-stripped and keeps
  upstream SUCCESS/column wording for grep compatibility.
- run_pytest.sh: make USE_FLAGTUNE overridable, group all knobs into a
  config section with Chinese comments, add start/end banners.
- README: document the warmup semantics, new plugins/env vars, and the
  A/B rule that both sides must use the same USE_FLAGTUNE.

_seed_plugin.py

@@ -27,13 +27,16 @@ def pytest_configure(config):
     try:
         import torch
     except Exception as exc:  # torch missing should never happen here, stay safe
-        print(f"[seed-plugin] torch unavailable, seeded {'+'.join(seeded)} only: {exc}",
+        from _term_style import tag
+        print(f"{tag('[seed-plugin]')} torch unavailable, "
+              f"seeded {'+'.join(seeded)} only: {exc}",
               file=sys.stderr)
         return
     torch.manual_seed(seed)
     if torch.cuda.is_available():
         torch.cuda.manual_seed_all(seed)
     seeded.append("torch")
-    print(f"[seed-plugin] manual_seed({seed}) for {'+'.join(seeded)} "
+    from _term_style import tag
+    print(f"{tag('[seed-plugin]')} manual_seed({seed}) for {'+'.join(seeded)} "
           "— reproducible benchmark inputs/cases",
           file=sys.stderr, flush=True)